How to Choose a Vitamin D Supplement

Vitamin D supplements can look alike on a results page, yet the labels differ in ways that matter: the form of vitamin D, the amount in a serving and the unit it is written in, whether anyone outside the company has checked what is in the bottle, and what the packaging promises. This guide sets out what to check before you buy, for healthy adults. If you are pregnant or breastfeeding, buying for a child, have kidney disease or take regular medicines, read the cautions near the end first.

The criteria come from named public sources: MedlinePlus, the NIH Office of Dietary Supplements (ODS), the Food and Drug Administration (FDA), the National Academies' Dietary Reference Intakes and the American Academy of Pediatrics (AAP). We do not rank products or rate brands. Amazon links on this page open searches built from the criteria, and you check each listing against its label.

First, ask whether you need one

Few foods contain much vitamin D, and sunlight helps the body make it, so a supplement is one option among several. MedlinePlus lists people who may need extra, including older adults, breastfed infants and people with dark skin, and advises checking with a health care provider about whether you need a supplement and how much. Our guide to who needs a vitamin D supplement covers the groups, sunlight and latitude, and blood tests.

Choose the form: D3 or D2

Supplements contain vitamin D3 (cholecalciferol) or vitamin D2 (ergocalciferol). MedlinePlus says both raise vitamin D in the blood, but D3 might raise it higher and for longer. A 2024 meta-analysis of 17 randomized trials in healthy adults found the same on average, though the difference was not seen in participants who mostly had overweight or obesity. The FDA's label-conversion guidance treats the two as bioequivalent for converting IU to mcg, so one conversion applies to both. Most listings are D3, and vitamin D3 softgels on Amazon (opens in a new tab) is a reasonable starting search.

For a plant-based diet, the Vegetarian Resource Group noted in 2011 that D3 is usually derived from lanolin in sheep's wool, with lichen-derived D3 an exception. Here is a search for vegan vitamin D3 on Amazon (opens in a new tab). Our guide to D3 and D2, drops and tablets has the detail.

Read the amount in mcg and know the IU

US labels must give vitamin D in micrograms (mcg), and the FDA allows international units (IU) in parentheses after it. The conversion is 1 mcg = 40 IU, so 10 mcg is 400 IU, 15 mcg is 600 IU, 25 mcg is 1,000 IU and 100 mcg is 4,000 IU. The FDA's own worked example of a supplement panel reads "Vitamin D 25 mcg (1,000 IU) 125%". The percentage is the % Daily Value, measured against a Daily Value of 20 mcg. Our guide to percent Daily Value explains that column.

The recommended amount for most adults is 15 mcg (600 IU) a day from all sources, and the upper limit is 100 mcg (4,000 IU). Our guide to vitamin D dose and upper limits sets out both. A search such as vitamin D3 25 mcg (1,000 IU) on Amazon (opens in a new tab) matches the words on a label. It is not a suggestion that this is the amount for you.

Pick a format you will take consistently

Softgels, capsules and tablets are the usual formats. Chewables and gummies suit people who dislike swallowing pills, so read the sugars and the ingredient list as you would for any other sweet; here is a search for vitamin D3 gummies on Amazon (opens in a new tab). Liquid drops let you measure small amounts. The AAP notes that some liquids give 400 IU in a single drop and others in one-half or one milliliter, so the dose depends on the product and you should read the label of the one you have. Vitamin D3 liquid drops on Amazon (opens in a new tab) is a search for them.

MedlinePlus adds that you absorb vitamin D better with a meal or snack that includes some fat. None of the sources we read rank one format above another, so choose by amount, verification and what you will actually take.

Look for outside verification

The FDA does not approve dietary supplements before they are sold and does not test them first; manufacturers and distributors are responsible for safety and labeling. That puts weight on checks you can make yourself. A 2013 research letter in JAMA Internal Medicine, reported by ScienceDaily, measured 55 bottles of over-the-counter vitamin D from 12 manufacturers bought in Portland, Oregon, plus a compounded product, and found contents from 9% to 146% of the amount on the label across the products tested, with variation among pills from the same bottle. The one manufacturer with the USP Verified Mark was generally more accurate, and the lead author said the mark may be worth looking for. The study is small and old, but it shows why a label amount is a claim to check.

Two voluntary programs are common on US labels. USP says its Verified Mark means the product contains the listed ingredients in the declared amounts, meets limits for certain contaminants, breaks down properly and is made under good manufacturing practices. NSF's certification program checks the label against the contents and tests for contaminants, and its Certified for Sport mark adds screening for substances banned in sport. Those descriptions are the programs' own, and a mark speaks to what is in the bottle, not to whether the supplement will do anything for you. Here are searches for USP Verified vitamin D3 on Amazon (opens in a new tab) and NSF certified vitamin D3 on Amazon (opens in a new tab). They match words only, so confirm the mark on the pack and in the program's own listing.

Read the rest of the panel

Check the serving size, because some products set a serving at two gummies or capsules. Then read the ingredient statement below the Supplement Facts panel. The FDA's labeling guide says ingredients not already named in the panel, such as fillers and other excipients, go there in descending order by weight, and one of its examples lists gelatin. If you avoid animal products, have an allergy or watch sugar, that line shows capsule shells, oils and sweeteners. Our guide to reading the Nutrition Facts label covers the panel on food.

Be wary of big claims

The FDA allows a supplement label to describe how a nutrient affects the body's normal structure or function, for example "calcium builds strong bones", if the label carries a statement that the FDA has not evaluated the claim and that the product is not intended to diagnose, treat, cure or prevent any disease. Only a drug can claim to treat or prevent a disease, and the FDA says a product sold as a supplement but represented that way is regulated as a drug. MedlinePlus describes vitamin D's role plainly: it helps the body absorb calcium, a mineral needed for normal bone formation. A listing that promises much more deserves caution.

Stay within the upper limit

The upper limit is 100 mcg (4,000 IU) a day for anyone age 9 and older, and the ODS says it covers food, drinks and supplements together, so a multivitamin and fortified milk count too. MedlinePlus says vitamin D toxicity almost always comes from taking too many supplements.

Who should speak to a clinician first

• Pregnant or breastfeeding. The FDA says pregnant or breastfeeding people should discuss supplements with their provider. MedlinePlus gives the recommended amount in pregnancy and breastfeeding as 15 mcg (600 IU), the same as for other adults, so check the vitamin D already in any prenatal vitamin.
• Babies and children. The AAP says babies younger than 12 months need 400 IU a day, that breastfed infants should get that as a supplement, and that older children need 600 IU. Ask your pediatrician, because liquids differ in strength.
• Kidney disease, kidney stones or high blood calcium. MedlinePlus says too much vitamin D can make the intestines absorb too much calcium, which can lead to high blood calcium, kidney damage and kidney stones. Ask your clinician before taking a supplement if any of these applies to you.
• Medicines. The ODS consumer fact sheet lists orlistat, which can reduce how much vitamin D the body absorbs; cholesterol-lowering statins, which might not work as well with high-dose vitamin D; steroids such as prednisone, which can lower blood levels; and thiazide diuretics, which could raise blood calcium too high. The FDA says to tell your provider about everything you take.
• Everyone. The FDA advises talking to your doctor, pharmacist or other health care professional before you use a supplement.

Where the links go

Links marked "on Amazon" open an Amazon search for the words in the link. Amazon decides what appears, and results can include products that do not meet the criteria above, so check each listing against the label.

Read next

• Who needs a vitamin D supplement: food, sunlight, latitude and blood tests.
• Vitamin D dose and upper limits: the recommended amounts, mcg and IU.
• Vitamin D3 vs D2, drops vs tablets: forms, formats and vegan options.

The label on the pack in front of you is the authority on dose, ingredients and warnings, ahead of any article, this one included. If you have a health condition or take medicines, ask your doctor or pharmacist before you start.